1. Field of the Invention
This invention relates to a folding station appended to a web-fed printing press, as in newspaper production, for cutting the printed paper web into sections and folding the successive web sections each in the middle into the form of signatures. More particularly, the invention deals with a jaw cylinder at the folding station which has sets of fixed and movable jaws arranged at circumferential spacings thereon for folding the web sections as they are thrust into the jaw cavities. Still more particularly, the invention pertains to a system for automatically adjusting the spacing between the fixed and movable jaws to the operating speed of the printing press.
2. Description of the Prior Art
The web sections to be engaged by the jaws on the jaw cylinder are subject to substantive change in thickness even in the limited case of newspaper production. The paper in use may itself vary in thickness. What is more, the pages of each signature to be produced can vary considerably in number as two or more webs are concurrently printed and superposed one upon another before being fed into the folding station for production of multiple-page signatures. The spacing between each set of fixed and movable jaws must be adjustable to such widely different thicknesses of the web sections to be folded, in order to create proper folds without doing any harm to the printed paper. The jaws must nevertheless capture the web sections firmly enough to avert accidental disengagement as the web sections are subsequently folded into signatures.
Japanese Patent Publication No. 7-55761 is hereby cited as prior art on the subject of jaw spacing adjustment. It teaches to sense the thickness of the printed web or webs being introduced into the folding station and to vary the spacing between the fixed and movable jaws accordingly.
More recently, however, such thickness-dependent adjustment of jaw spacing has proved insufficient for the proper functioning of the jaw cylinder as a result of remarkable rise in the running speed of the printing press. Let it be supposed that the jaw spacing is now set properly for a given web thickness and at a given running speed of the press. Then, according to the prior art thickness-dependent adjustment of jaw spacing, the web sections were easy to fall off the jaws when the press speed was made higher, particularly in the case of production of multiple-page signatures.
Let us now briefly study the makeup of the folding station of the rotary printing press in order to learn in some more detail the problems involved in jaw spacing adjustment. The folding station has a cutter cylinder and a folding cylinder in addition to the jaw cylinder, which cylinders are all in constant rotation during the progress of printing. The printed web of paper is first wrapped around part of the folding cylinder and, while traveling thereover, cut into successive sections by cutting blades on the cutter cylinder which is held against the folding cylinder via the web. The folding cylinder is equipped with elongate folding blades each extending parallel to the folding cylinder axis and arranged at circumferential spacings thereon. Each folding blade is movable radially of the folding cylinder.
Pushed off the surface of the folding cylinder by one of the folding blades, each web section has its midpart inserted in one of the elongate jaw cavities which are cut in the surface of the jaw cylinder at circumferential spacings. The midpart of the web section that has been pushed into the jaw cavity is therein engaged, together with the folding blade, between the fixed and movable jaws as the movable jaw is closed against the fixed jaw, and thereby folded along the centerline of the web section. The web section is subsequently carried away from the surface of the folding cylinder by the jaw cylinder as these cylinders continue rotation in opposite directions. The folding blade withdraws from between the fixed and movable jaws just after the web section has been thereby engaged, so that the web section is folded along the centerline while being carried away from the folding cylinder.
When the web section is pulled off the folding cylinder as above after having its midpart captured by the jaws, the leading half of the web section must travel in sliding contact with the folding cylinder. An inertial force will then act on the web section, tending to pull the web section out of engagement with the jaws in opposition to spring pressure being exerted on the jaws. The greater the mass of the web section, or the more the number of webs superposed, the stronger will be the centrifugal pull of the web section. Actually, the web sections fell off the jaws in the worst case.
Obvious solutions to this problem might be to make the jaw spacing narrower, to employ heavier springs for the movable jaws, or both. These solutions are unsatisfactory because, at lower running speeds of the press, ink offset would occur between the contacting surfaces of the web sections being folded.
The present invention seeks, in connection with the folding station of a rotary printing press, to automatically adjust the jaw spacing to the running speed of the printing press in order to minimize the risks of accidental disengagement of the web sections from the jaws and of ink offset between their contacting surfaces.
Another object of the invention is to make automatic adjustment of the jaw spacing depending not only upon the running speed of the press but also upon the mass of each web section to be folded or the pages of the signatures to be made.
In summary the present invention concerns a speed-responsive jaw spacing adjustment system for a jaw cylinder at the folding station of a web-fed printing press where one or more webs of printed paper are cut into successive sections, and each web section folded into a signature. The jaw cylinder is conventionally furnished with a fixed and a movable jaw, the latter being movable toward and away from the former for engaging and folding each web section as its midpart is inserted therebetween. The fixed and movable jaws are, moreover, mounted to separate, independently movable parts of the jaw cylinder which are coupled to jaw spacing adjustment means to permit adjustment of the spacing therebetween in any operating phase of the movable jaw relative to the fixed jaw. The jaw spacing adjustment means have their own drive means including a bidirectional electric drive motor such as a stepper motor.
For controllably energizing the drive motor according to the running speed of the printing press, the jaw spacing control system comprises a press speed circuit for providing a press speed signal indicative of the speed at which the web is currently being fed into the folding station, and a jaw spacing circuit for providing a jaw spacing signal indicative of the current actual spacing between the fixed and the movable jaw. Connected to these circuits is a jaw spacing adjustment circuit which puts out, in response to the incoming press speed signal and jaw spacing signal, a jaw spacing adjustment signal for adjustment of the jaw spacing to the current press speed. The jaw spacing adjustment circuit has its output connected to the drive motor for causing the same to drive the jaw spacing adjustment means in response to the jaw spacing adjustment signal.
More specifically, the jaw spacing adjustment circuit responds to the incoming press speed signal by determining an optimal jaw spacing for the current press speed and compares this optimal jaw spacing with the actual jaw spacing indicated by the jaw spacing signal. If a difference proves to exist between the desired and the actual jaw spacing, then the adjustment circuit produces the jaw spacing adjustment signal for elimination, or reduction to a tolerable range, of that difference.
Preferably, in cases where the printing press is designed for concurrent printing of a variable number of webs for production of signatures of a variable number of pages, the jaw spacing may be adjusted not only to the press speed but also to the number of webs to be processed jointly. Toward this end there may be additionally provided an input device for inputting data indicative of how many webs are processed simultaneously, and a memory for storing a table indicative of desired jaw spacings for various combinations of a series of different press speeds and a series of different web numbers. Inputting the web number data in addition to the press speed signal and actual jaw spacing signal, the jaw spacing adjustment circuit can be made to read out from the memory the desired jaw spacing suiting the particular combination of the current press speed and current web number.
Thus, at whatever speed the press may be run, the jaw spacing is automatically readjusted to that press speed for engaging and folding the web sections under optimum pressure. The web sections of any of predetermined different thicknesses are not to accidentally fall off the jaws at high press speed, nor is ink offset to occur between their contacting surfaces at low press speed. All in all, the jaw spacing adjustment system has proved to contribute immensely to the production of printings of invariably high quality and to the reduction of press downtime.
The above and other objects, features and advantages of this invention will become more apparent, and the invention itself will best be understood, from a study of the following description and appended claims, with reference had to the attached drawings showing the preferred embodiment of the invention.